The detail gun the Paul mentioned works well.
Used to spray full sized planes with dope about a hundred yrs ago, well, in the late 50s.
Pressurized in a 5 gallon pail. Mercerized cotton cloth for covering. Pinned on, sewn together, and shrunk with water, then doped with nitrate dope, sanded and finished with butyrate dope.
Pretty much the same with a model.